Conventional color diffusion transfer photosensitive materials are classified into two groups by film unit structure as of peel-apart type and no peel-apart type. In a photosensitive material of the peel-apart type, a light-sensitive layer unit and a dye image-receiving layer unit are coated on separate supports, and its photosensitive and image-receiving elements are brought into face-to-face contact with each other after imagewise exposure. Then, a processing solution is spread between those elements, and thereafter is peeled apart the dye image-receiving element. Thus, dye images transferred to the dye image-receiving layer are obtained.
However, the material of the above-described type has a problem such that, when the dye image-receiving element is delaminated after the prescribed time (exceeding the time at which the image formation is completed), dyes remaining in the photosensitive element are further transferred to cause color balance loss, stains on the white background and so on.
As for the photosensitive materials of no peel-apart type, on the other hand, a dye image-receiving layer and silver halide emulsion layers are sandwiched between a transparent support and another support. In one structure, those layers all are coated on the transparent support; while in another structure the dye image-receiving layer is coated on the transparent support and the emulsion layers are coated on the other support. Further, in order to view dye images transferred to the image-receiving layer by reflected light, the former structure is designed so as to have a white light-reflecting layer between the image-receiving layer and the emulsion layer unit, and the latter structure is designed so that a processing composition containing a white pigment can be spread between the image-receiving layer and the silver halide emulsion layer unit.
However, the photosensitive materials of the no peel-apart type suffer an appreciable change in image density with the lapse of time, because it takes a good long time for the dyes released from the silver halide emulsion layers to finish fixing to the image-receiving layer. In this respect, it is desirable for them to undergo a decided improvement.
As a means of solving the above-described problems, there are disclosed a method of providing a dye-capturing layer, which comprises a quaternary salt type polymer latex, as the outermost layer of a transparent cover sheet in JP-A-3-53248 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), an art of providing a dye-capturing layer inside a timing layer or on the base side of a timing layer in U.S. Pat. No. 3,930,864, and an art of providing a dye-capturing layer between an image-receiving layer and a dye-producing layer in U.K. Patent 1,537,079.
However, such methods cannot accomplish sufficient effects. In addition, they have a problem of causing a decrease in transferred image density. Thus, arts of preventing the transferred image density from changing with the lapse of time without accompanied with a drop in transferred image density are desirable to be developed.